The position of a boom of a backhoe is commonly controlled by a pair of hydraulic jacks connected between a main support frame and a boom support frame. The boom is swung in an arcuate path about its pivotal connection to the main frame generally by extending one of the jacks and retracting the other jack. The boom control circuit is normally provided with a pair of line relief valves and a pair of makeup valves connected to the respective lines connecting a control valve to the hydraulic jacks. The line relief valve functions to vent fluid from one of the lines when excessive pressure is generated therein while the makeup valves function to provide makeup fluid to a line if it becomes cavitated.
One of the problems sometimes encountered therewith occurs when the swinging motion of the boom is abruptly stopped by moving the control valve to its neutral position and the inertia of the boom and the other components supported thereby generates fluid pressure in one of the lines sufficient to open the relief valve thereby allowing fluid to be expelled from that line. This results in the other line being cavitated. While the makeup valves directs most of the expelled fluid into the cavitated line, some of the expelled fluid leaks past other valves in the system and not all of the expelled fluid is reclaimed such that a void is created on one side of the hydraulic jacks. This void then allows the boom to rebound or bounce from side to side a small amount until the inertia energy is dissipated. This is a performance deficiency sometimes referred to as "swing wag".
The present invention is directed to overcoming the problem as set forth above.